Abstract
The analysis of common methods and systems of thermal protection of electric motors is carried out. It is shown that the most promising of them are the methods based on monitoring the active resistance of the stator winding of an electric motor, the value of which is uniquely determined by its temperature. However, such methods require either the input of a constant measuring current, or the selection of the indicated parameters by an algorithmic way from the operating variables. A new method of thermal protection of AC electric motors is proposed. The method is based on the fact that a change in the active and / or reactive components of the impedance of the winding due to a change in its temperature causes a corresponding change in the angle between the vectors of phase voltages and currents. This provides thermal protection by controlling the change in the specified angle. The corresponding version of the structural block diagram of the device that implements the proposed method of thermal protection has been developed. Experimental studies have been carried out, the results of which have confirmed the efficiency and effectiveness of the proposed technical solution.
Keywords
AC motor, thermal model, soft start device, active resistance of the stator winding, synchronous detector, in-phase and quadrature components of the supply voltage, phase difference between voltage and current vectors.
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